A motor may operate without any position feedback and rely on a motor's inherent characteristics to control the position of the rotor by energizing particular stators of the motor. This manner of motor operation may typically be found in stepper motors, wherein the rotor of a motor rotates by a specific number of degrees in response to input electrical signals to energize particular stators of such motors.
Stepper motors typically convert digital pulse inputs to analog output rotor movement. Typically, in response to an input pulse of electrical signal, the rotor of a stepper motor rotates by a design-specified number of degrees, or a step. Stepper motors are typically classified as permanent magnet, variable reluctance, or hybrid. A permanent magnet stepper motor typically has as its rotor a permanent magnet, whereas a variable reluctance stepper motor may have a toothed block of a magnetically soft (or ferromagnetic) rotor. A hybrid stepper motor has typically an axial permanent magnet at the middle of the rotor and ferromagnetic “teeth” at the outer portion of the rotor.
Operating stepper motors without any position feedback may cause problems in situations where the rotor “lags” behind the intended rotor position by being a number of steps, or in steps being “lost” and never recovered if the rotor lags behind the intended position too much. Lagging may occur, for example, if a rotor is attached to a large load and the acceleration force of the motor is too low to rotate the rotor fast enough to respond to a control input signal before a next input signal is received. Further, without any positional feedback, resonance problems may occur leading to a “stall” condition, such as when the magnetic field created by the stators of the motor is such that it holds the rotor in place rather than rotating it, cannot be detected and corrected by a motor controller. Additionally, even if resonance does not lead to a stall conditions, undesirable oscillations would result from the resonance.
Positional feedback sensors may be incorporated into a motor to monitor the position of the rotor optically, but such systems may be complicated to install and maintain, and furthermore may require substantially more control circuitry or software modules to implement.
There is a need for a system and method for obtaining feedback information and controlling motor operation without using positional feedback sensors.
The operation of an electromagnetic motor is typically via the generation of one or more electromagnetic fields that operate to cause rotation of a rotor of the motor. There is a need for a system and method for controlling the electromagnetic fields generated in an electromagnetic motor to improve performance.